1. Field of the Invention
The present invention relates to a distribution apparatus and a quench zone mixing apparatus (or device) that may include the distribution apparatus, both of which are suitable for efficiently mixing and redistributing reactants across the horizontal cross-section of a vertical reaction vessel.
2. Discussion of Related Art
Many catalytic processes are carried out in reactors that contain a series of separated catalytic beds. Frequently, in such processes, quench zone mixing devices are advantageously located to provide rapid and efficient mixing of the fluid streams being processed in the reactor with a cooler fluid stream supplied from an external source. Consequently, the temperature of the process stream entering the successive catalyst beds can be controlled. One skilled in the art will appreciate that the better the mixing of the reactant streams, the better the temperature and reaction can be controlled. As a result, the overall performance of the reactor will be better.
Examples of quench zone mixing devices include U.S. Pat. Nos. 3,353,924, 3,480,407, 3,541,000, 4,669,890, and 5,152,967. Some of these devices are complicated and are prone to plugging. Others need a relatively large vertical space to ensure the desired degree of mixing. Still others create an undesirably high pressure drop. Consequently, there is a continuing need for a suitable quench zone mixing device that can efficiently mix fluid streams in a low vertical space with an acceptably low pressure drop.
Typically, the quench zone mixing devices are located above an associated fluid distribution system; for example, a horizontally disposed distribution plate or tray. The distribution plate collects the fluid (vapor and liquid), uniformly distributes it across the plate and discharges the fluid on to the catalyst bed. Such distribution tray may contain a number of xe2x80x9cbubble capxe2x80x9d assemblies which may be disposed over one or more openings in the distribution tray. The bubble cap provides intimate mixing of the vapor and liquid before the mixed phase fluid is distributed across the catalyst bed.
Examples of distribution trays include U.S. Pat. Nos. 2,778,621, 3,218,249, 4,960,571, 4,836,989, 5,045,247, 5,158,714 and 5,403,561. Although one or more of these designs may be acceptable, there is still room for improvement, particularly in providing a uniform distribution of vapor and liquid phases into contact with the catalyst in the reactor vessel.
It is an object of the invention to provide a distribution apparatus that includes a redistribution tray (also referred to herein as a xe2x80x9credistribution platexe2x80x9d). It is another object of the invention to provide a quench zone mixing apparatus (also referred to herein as the xe2x80x9cquench zone mixing devicexe2x80x9d) that includes a swirl chamber, a rough distribution network disposed underneath the swirl chamber, and, preferably, a distribution apparatus disposed underneath the rough distribution network. It is to be understood that the distribution apparatus can be associated with the quench zone mixing device or can be used separately from the quench zone mixing device; for example, at the top of the reactor vessel.
The distribution apparatus includes a redistribution plate (also referred to herein as a xe2x80x9cplatexe2x80x9d) having a plurality of apertures and a plurality of bubble caps with at least some of the bubble caps associated with at least some of the apertures. In one embodiment, a plurality of drip trays are substantially horizontally disposed underneath the redistribution plate. At least some of the drip trays are associated with at least some of the bubble caps. The drip trays receive fluids exiting the associated bubble caps and distribute them through at least one discharge port provided on the bottom of the drip tray. In another embodiment, the drip trays have at least two discharge ports to multiply the fluid drip stream received from the bubble cap and symmetrically distribute the fluid across the catalyst surface.
Instead of the drip trays, at least one deflector baffle, and preferably a plurality of deflector baffles, may be placed below the redistribution tray. Preferably at least some of the deflector baffles are associated with at least some of the bubble caps.
As noted above, the quench zone mixing apparatus includes a swirl chamber. The swirl chamber is adapted to receive fluids from upstream in the reactor (such as those exiting a catalyst bed located above the swirl chamber). Preferably, the swirl chamber is substantially cylindrical. The swirl chamber includes a wall disposed between a ceiling and a floor. The wall has a plurality of openings, such as inlet openings, that provide a means of fluid communication into the swirl chamber. The floor surrounds an orifice, which provides a means for fluid to exit the swirl chamber. Preferably, a weir is provided about the periphery of the orifice. Baffles are located inside the swirl chamber which stabilize the vapor and liquid phase vortices, reduce the required overall height of the swirl chamber, provide a wide operating range for vapor and liquid throughput, and promote turbulence/mixing within each of the fluid phases. At least some of the openings have a baffle associated with the openings.
The rough distribution network is disposed beneath the swirl chamber to receive fluids from the swirl chamber. The rough distribution network includes a splash plate and radially outwardly extending channels. The splash plate is adapted to collect fluids from the swirl chamber and radially outwardly distribute them through the channels. Preferably, the channels include side walls with spaced apart notches to allow fluid to exit the channels. Fluids exiting the channels fall onto a distribution apparatus disposed beneath the rough distribution network.
Preferably, the distribution apparatus includes the redistribution plate substantially horizontally mounted below the rough distribution network and the swirl chamber. The redistribution plate extends substantially across the entire cross-section of the vessel to separate an upper section of the vessel from a lower section. The redistribution plate comprises a plurality of apertures and a plurality of bubble caps associated with the apertures of the redistribution plate. More preferably, a bubble cap is associated with each aperture to provide the sole means of fluid flow through the plate.
The bubble caps include a riser and a spaced apart cap. The riser has a top and a bottom and the riser is secured near the bottom to the redistribution plate. A passageway is defined between the top and bottom and provides a means of fluid communication across the redistribution plate. Preferably, the cap has a plurality of spaced apart slots to allow the flow of fluids through the cap and into the annulus defined by the cap and the riser.
In a preferred embodiment, the ceiling of the swirl chamber is closed. A liquid collection tray, preferably frusto-conically shaped, surrounds the swirl chamber and is sloped so that the one end adjacent the inlet openings is lower than the other end adjacent to the vessel wall. Fluid exiting the preceding catalyst bed falls onto the liquid collection tray or onto the ceiling of the swirl chamber where it is directed onto the liquid collection tray and through the inlet openings. Baffles are located inside the swirl chamber adjacent the openings and in communication with the openings to receive and direct incoming fluid circumferentially about the swirl chamber. In this preferred embodiment, the orifice is centrally located and provides the sole means for fluid to exit the swirl chamber. Additional baffles, i.e., wall baffles and internal baffles (the latter located on the floor of the swirl chamber), may also be included.
In another preferred embodiment, a quench fluid system is provided to introduce quench fluid into or above the swirl chamber. The quench fluid system may include a feed pipe in communication with a concentric manifold that surrounds the swirl chamber. A plurality of quench fluid laterals in fluid communication with the manifold extend radially inward and terminate with nozzles that extend into the swirl chamber. The nozzles are located adjacent and below the baffles and have openings to direct quench fluids into the fluid stream exiting the baffles.
Alternatively, the quench fluid system may include a feed pipe which introduces the quench fluid directly (without a manifold) into the swirl chamber or into an area above the swirl chamber.
In another embodiment of the present invention, a reactor is provided with the quench zone mixing apparatus of the present invention interposed between two catalyst beds. Preferably, the quench zone mixing apparatus is supported within a vessel of the reactor by a support structure that includes a concentric hub, which may be formed to act as a torsion tube, and at least a first set of radial beams extending radially outward from the hub and terminating at a support ring that is attached to the reactor vessel wall.
In particular, the radial beams comprise a flange that supports the redistribution tray and a web of the beams preferably includes a plurality of openings to allow the passage of fluids across the vessel. In addition, the webs also carry the channels. The radial beams also support the swirl chamber and, in the area between the wall of the swirl chamber and the vessel wall, the radial beams may have a vertical height that slopes downward from the vessel wall to the swirl chamber wall. Specifically, the radial beams at the swirl chamber wall have a vertical height at about the bottom of the openings on the swirl chamber wall and at the vessel wall the radial beams have a vertical height greater than at the swirl chamber wall. The liquid collection tray is provided on the top of the radial beams in the area between the swirl chamber wall and the vessel wall to create a downwardly sloping conical surface. As in other embodiments, the liquid collection tray is preferably frusto-conical shaped and it surrounds the swirl chamber.
Alternatively, a first set of radial beams having a single vertical height may be provided with a second set of radial beams located vertically above the first set. In this case, the top of the second set of radial beams is downwardly sloped in the same fashion as described above. In either case, the liquid collection tray collects fluid from the ceiling of the swirl chamber and from the catalyst bed above and directs it through the openings in the swirl chamber.
In a preferred embodiment, a first set of radial beams having a single vertical height is used to support the swirl chamber and distribution channels. Additionally, a support ring is attached to the outside wall of the swirl chamber at a location just below the inlet openings. A second support ring is attached to the vessel wall at a location approximately equal to the elevation of the swirl chamber ceiling. The liquid collection tray is provided on top of the support rings in the area between the vessel wall and the swirl chamber to preferably create a frusto-conical shape that directs fluids from the catalyst bed above toward the swirl chamber inlet openings. The ring at the wall provides support for the liquid collection tray and a sealing surface to prevent fluids from bypassing the swirl chamber.
The present invention also contemplates an improvement in known quench zone mixing devices wherein a rough distribution network is interposed between a mixing chamber (or a swirl chamber) and a distribution apparatus. The present invention therefore provides a reactor that includes the quench zone mixing apparatus of this invention, which comprises a mixing chamber and a distribution apparatus. In particular, the improvement comprises a rough distribution network disposed between the mixing chamber and the distribution apparatus, the rough distribution network comprising a splash plate in fluid communication with outwardly extending channels. Preferably, the channels extend outward radially from the splash plate. The splash plate preferably has apertures and the channels preferably include side walls with spaced apart notches to allow fluid to exit the channels.
The invention is also directed to a bubble cap which comprises: a riser having a lower end located within and extending through an aperture in a plate of the distribution apparatus and a top end to define a passageway between the ends, the passageway including an inlet and an outlet; a cap located over the top end of the riser, the cap having a top portion and a downwardly extending skirt portion; a spacer located between the riser and the cap to maintain a gap between the top end of the riser and the cap; and a deflector baffle placed below the outlet of the passageway.
The deflector baffle may have any desired construction, and it redirects the majority of the fluid flowing downwardly from the riser passageway, so that the fluid forms a relatively wide spray pattern over the downstream catalyst bed (as compared to the fluid flow pattern from a bubble cap without the deflector baffle).
Additionally, the invention is directed to a bubble cap comprising: a riser having a lower end located within and extending through an aperture in the plate of the distribution apparatus and a top end to define a passageway between the ends; a cap located over the top end of the riser, the cap having a top portion and a downwardly extending skirt portion; at least one spacer located between the riser and the cap to maintain a gap between the top end of the riser and the cap; and a plurality of riser vanes located between the top end of the riser and the top portion of the cap. An annulus (xe2x80x9cbubble cap annulusxe2x80x9d) is created between the riser and the cap. The riser vanes are preferably flush against the underside of the bubble cap top wall. The riser vanes are spaced from each other to form vane passageways. Preferably, the vane passageways are the only (or sole) means of fluid communication between the bubble cap annulus and the riser passageway.
A bubble cap may also include the deflector baffle and the riser vanes.
The deflector baffle and/or the riser vanes (as described herein) may also be included in a bubble cap of any other construction.
The present invention also contemplates the use of a distribution apparatus where the distribution apparatus is not associated with the quench zone mixing apparatus i.e., the distribution apparatus is used in addition to the quench zone mixing apparatus or used in a reactor that does not have a quench zone mixing apparatus. In this embodiment, the distribution apparatus may be provided above a catalyst bed. For example, the distribution apparatus may be provided at the top of the reactor or between successive catalyst beds. The distribution apparatus will include a redistribution plate and a plurality of bubble caps, as described above. In addition, the distribution apparatus may also be provided with a plurality of drip trays, as described above. In another embodiment, the drip trays may be omitted and at least one deflector baffle included in the distribution apparatus, as described above. The riser vanes may be included in any of the bubble caps. In this embodiment, the distribution apparatus is usually called a xe2x80x9cdistribution trayxe2x80x9d.
The present invention also contemplates the use of a quench zone mixing apparatus in a process for contacting a first fluid with a second fluid, wherein the first and second fluids may be liquid and/or gas. Preferably, the process occurs in a portion of a reactor between two successive spaced apart beds of particle form solids, e.g., catalyst particles. In one embodiment, the invention broadly includes introducing a first fluid into the reactor; transporting the first fluid through a first catalyst bed; collecting the reaction product from the first catalyst bed and transporting it through the quench zone mixing device where it is further mixed and reacted with a quench fluid (xe2x80x9csecond fluidxe2x80x9d) to form a further reaction product that is distributed onto the surface of a second bed, including catalyst particles, located downstream from the first catalyst bed. In one particular application of this embodiment, hydrotreating and hydrocracking of relatively heavy petroleum hydrocarbon stocks, the first fluid is a hot mixture of gas and liquid and the second fluid is a cold gas or cold liquid.
In a particular embodiment, the process is directed to a two phase downflow reactor. The process includes introducing a first fluid, such as liquid and gas reactants, into the reactor at a location above a swirl chamber. Preferably, the first fluid is introduced in an upper section of the reactor. The first fluid is then introduced into the swirl chamber. A second fluid, e.g., a quench gas, is introduced into the swirl chamber and contacts the first fluid to form a swirl chamber fluid mixture. The swirl chamber fluid mixture exits the swirl chamber and is collected by a rough distribution network where the swirl chamber fluid mixture is radially distributed over a splash plate and outwardly extending channels. Subsequently, a fluid mixture exiting the channels is conducted to a distribution apparatus. The distribution apparatus includes a redistribution plate with a plurality of apertures and a plurality of bubble caps with at least some of the bubble caps associated with at least some of the apertures. The fluid mixture is transported through the redistribution plate to form a redistribution plate fluid mixture. The redistribution plate fluid mixture is eventually transported to a downstream section of the reactor.
In one embodiment of the process, a deflector baffle is associated with at least some of the bubble caps. Also, riser vanes may be included in at least some of the bubble caps.
In another embodiment of the process, before the redistribution plate fluid mixture is transported to the downstream section of the reactor, it is collected on a plurality of substantially horizontal drip trays with at least some of the drip trays which are located underneath the plate and associated with at least some of the bubble caps. The collected redistribution plate fluid mixture is distributed through at least one discharge port in the drip trays and some separation of the gas from the liquid takes place on the drip trays.
The invention is also directed to a process for transferring a fluid from a first bed of a reactor to a second bed of a reactor, located downstream from the first bed. The process comprises introducing a fluid from the first bed of the reactor into a swirl chamber. Subsequently, the fluid is removed from the swirl chamber, and is introduced into a rough distribution network including a splash plate and outwardly extending channels. Then, the fluid is conducted from the rough distribution network to a distribution apparatus, which includes a redistribution plate with a plurality of apertures and a plurality of bubble caps. At least some of the bubble caps are associated with at least some of the apertures. The fluid is then transported through the redistribution plate to the second bed of the reactor. The fluid may include a gas, a liquid or a mixture of liquid and gas. A quench fluid, liquid or gas, may also be introduced separately into the swirl chamber.
The invention is also directed to a process for redistributing a fluid within a reactor. The process includes collecting the fluid on a distribution apparatus and distributing the fluid to a downstream section of the reactor in a substantially even fashion across the cross-section of the reactor. The distribution apparatus includes a redistribution plate with a plurality of apertures and a plurality of bubble caps, with at least some of the bubble caps associated with at least some of the apertures. In one embodiment, a plurality of substantially horizontal drip trays are located underneath the plate and associated with at least some of the bubble caps. Consequently, the fluid is collected on the surface of the redistribution plate and transported through the plate, to a downstream section of the reactor. If the drip trays are included, the fluid is transported through the plate onto the drip trays where it is transported to a downstream section of the reactor. In another embodiment, a deflector baffle is associated with at least some of the bubble caps Further, riser vanes may be included in at least some of the bubble caps.
The invention is also directed to a method of operating a swirl chamber which includes: a liquid collection tray; a wall disposed between a ceiling and a floor, the floor including an orifice which provides a means of communication out of the swirl chamber, the wall defining an inside of the swirl chamber; a plurality of openings (also referred to as xe2x80x9cinlet openingsxe2x80x9d), in the wall, which provide a means of fluid communication into the swirl chamber; a plurality of baffles (or first baffles) located inside the swirl chamber and in communication with the openings to receive and direct incoming fluid circumferentially about the swirl chamber. The method comprises introducing a fluid into the swirl chamber through the openings and directing the fluid onto the first baffles; subsequently, the fluid is directed from the first baffles onto the floor and towards the orifice, in such a manner that at least one of the first baffles is partially submerged by the fluid.
The apparatus and process of the present invention may be particularly applicable for use in fixed bed catalytic processing systems for hydrotreating, and hydrocracking, of relatively heavy petroleum hydrocarbon stocks. Such processing systems may use reactors with one or more vertically spaced catalyst beds. Although the invention may be particularly applicable for use in hydrogen treatment of hydrocarbons, the process and apparatus are not limited to such use and can be used in any system where the mixture of a vertically flowing, liquid and a vertically flowing, gas, or a lighter liquid and heavier liquid, is desired. For example, the invention may also be used in aromatic saturation, catalytic dewaxing and hydrofinishing operations.
The quench zone mixing apparatus may be placed in any suitable location in a reactor vessel. For example, it may be placed at the top of the reactor, so that any fluid entering the reactor will contact the quench zone mixing, apparatus before it contacts any other internal reactor devices. Alternatively, the quench zone mixing apparatus may be placed downstream from any internal reactor devices, such as internal catalyst beds.
For purposes of exemplification and illustration, a range of parameters is given below for some specific processing, systems for hydrotreating, and hydrocracking relatively heavy petroleum hydrocarbon stocks in which the apparatus and process of the present invention can be used. Such processing systems typically use reactors having inside diameters of 5 to 20 feet with about 2 to 5 vertically spaced catalyst bed spaces with lengths of 5 to 50 feet, and use catalysts typically having particle sizes of {fraction (1/32)} inch to xc2xc inch.
As pointed out in greater detail below, the quench zone mixing apparatus of this invention provides important advantages. The design of the invention apparatus minimizes the overall vertical height of the quench zone mixing apparatus. As a result, the overall vertical height of the reaction vessel can be decreased, thereby reducing the capital cost of the vessel. At the same time, intimate mixing and thermal equilibration is achieved while maintaining only a moderate pressure drop across the device.
The term xe2x80x9cfluidxe2x80x9d as used in the specification and claims is meant to include both liquids and gases. The term xe2x80x9cvaporxe2x80x9d and xe2x80x9cgasxe2x80x9d are used interchangeably herein.